Approximately 5 percent of infants born to mothers with chronic hepatitis C virus (HCV) become infected with the virus. When the infection actually occurs and the mechanism of maternal-fetal transmission have not been established. A higher incidence of infection exists in children born to mothers who are concurrently infected with human immunodeficiency virus (HIV). One issue with HCV transmission is whether the virus can be transmitted from mother to infant through breast milk, and the few published studies to date have produced conflicting results. Polywka and colleagues conducted a prospective study to evaluate the risk of HCV transmission from mother to infant through breast milk.

Mothers with confirmed HCV infection who tested negative for HIV were enrolled in the study. Breast-milk samples were obtained between day 1 and day 73 after delivery. Serum samples were obtained from the mothers between 59 days before and 73 days after delivery, although the mean time of collection was 2.1 days postpartum. The majority of samples of breast milk and serum were collected within one week of each other. Serum samples for HCV were obtained from 76 newborn infants during the first week of life and again between one and three months of age. In 38 infants, additional serum samples were obtained at follow-up visits for as long as 28 months.

The serum samples of mothers and infants were tested for antibodies to HCV by standard enzyme immunoassay. Confirmatory testing was performed using the immunoblot assay. The fresh serum or breast-milk samples were tested for HCV RNA with the polymerase chain reaction technique. The breast-milk samples were determined to be negative if at least two or three assays were negative compared with a positive control specimen.

All 76 infants of the 73 HCV-infected mothers were breast-fed. None of the breast-milk samples from the women was positive for HCV RNA. All maternal serum samples tested for antibodies to HCV were confirmed positive, and approximately 60 percent of mothers tested for HCV RNA had HCV viremia. During the follow-up component of the study, 75 of the infants remained negative for HCV RNA. One child, who was infected, tested negative at day 3 but had a positive HCV RNA assay at 27 days of age. Testing for antibody to HCV revealed that it took from three to 28 months for the infant to lose maternal antibodies to HCV, although the mean was nine months.

The authors conclude that HCV is not transmitted via breast milk; therefore, breast-feeding by an HCV-infected mother does not pose a risk to the infant. It is not necessary to prohibit HCV-positive mothers from breast-feeding. In their discussion, the authors cite another study that found HCV RNA in a large percentage of samples of colostrum, but no new pediatric infections were found in those children who were breast-fed.